Field of the Invention
An apparatus for manufacturing cement clinker is such as the equipment for preheating, precalcining, calcining, sintering and cooling, hereinafter referred to as an apparatus.
A first aspect of the present invention relates to a cement clinker manufacturing apparatus capable of lowering the temperature at which cement clinker is sintered.
A second aspect of the present invention relates to an improvement in a cement clinker manufacturing apparatus.
A third aspect of the present invention relates to an improvement in an apparatus for operating a sintering furnace of a cement clinker manufacturing apparatus.
A fourth aspect of the present invention relates to a jet fluidized bed granulating furnace having an improved perforated-plate type distributor.
A fifth aspect of the present invention relates to an improvement in an apparatus for injecting raw material of cement into a jet fluidized bed furnace.
A sixth aspect of the present invention relates to an apparatus for injecting granular raw material into any one of a variety of fluidized bed furnaces typified by a jet fluidized bed granulating furnace of raw material of cement.
A seventh aspect of the present invention relates to a jet fluidized bed granulating furnace for use as equipment for manufacturing cement clinkers (lumps before grinding state as to be formed into cement), the jet fluidized bed granulating furnace being capable of controlling the size of granulated material.
Hitherto, Portland cement clinker has been sintered at temperatures of 1400 to 1600.degree. C. in a rotary kiln (a rotary sintering furnace). That is, the Portland cement clinker has been intended to be sintered at 1500.degree. C. In this case, the sintering temperature allowance is about 50 to 100.degree. C., causing the cost of energy to be raised excessively to maintain the foregoing sintering temperature. What is worse, a heavy burden must be borne to get rid of pollution.
A conventional cement clinker manufacturing apparatus, as shown in FIG. 33, comprises a pre-heating unit 1 formed by a plurality of combined pre-heating furnaces, a pre-calciner 2 for pre-calcining raw material pre-heated in the pre-heating unit 1, a rotary kiln 3 that sinters the pre-heated raw material to form clinker, a clinker cooler 4 for cooling sintered clinker and a forced blower 5 for supplying cooling air to the clinker cooler 4.
The cooled cement clinker is then conveyed to a producing process (omitted from illustration), in which the cement clinker is ground and classified, so that a cement clinker product is manufactured.
The cement clinker is sintered in the cement clinker manufacturing apparatus in such a manner that the raw material of the cement clinker is heated to 800.degree. C. to 900.degree. C. in the pre-heating unit 1 and the pre-calciner 2, and then the hot raw material is charged into the rotary kiln 3 as to be heated to about 1500.degree. C. Since the heat conductivity to the raw material is low in the rotary kiln 3, it takes 10 minutes or longer to heat the cement clinker to 1300 to 1400.degree. C. In this case, the temperature rise rate is about 50.degree. C./minute or lower.
The foregoing sintering technology using the conventional manufacturing apparatus sinters cement clinker at about 1500.degree. C. It would be desirable to sinter the cement clinker at a lower temperature of about 1300 to 1400.degree. C. in order to save energy needed in the manufacturing apparatus and to reduce pollution by decreasing nitrides and oxides. However, sintering of the cement clinker at the low temperature needs addition of chlorine flux or lengthening the sintering time. Therefore, the pollution prevention and cost reduction cannot be realized as desired. What is worse, there arises a first problem in that mortar and concrete suffer from unsatisfactory strength.
A conventional cement clinker manufacturing apparatus has been disclosed (for example, in Japanese Patent Unexamined Publication No. 62-230657). According to this disclosure, the apparatus comprises a suspension pre-heater, a single-nozzle spouted bed granulating furnace, a fluidized bed sintering furnace and a cooling unit, wherein a plurality of opposing burners are disposed in the lower portion of the spouted bed granulating furnace to form a local hot region in the spouted bed, and the pre-heated raw material is charged onto the local hot region.
The cement clinker manufacturing apparatus is formed by the single-nozzle spouted bed granulating furnace and the fluidized bed sintering furnace which are combined with each other. The cement clinker manufacturing apparatus requires the prevention of directly dropping raw material powder through a throat of the spouted bed granulating furnace which results from raising the flow velocity. If the flow velocity is raised, the amount of undesirable discharge of raw material powder from the spouted bed granulating furnace increases. Therefore, there arises a problem of unstable operation occurring due to circulation of fine powder and another problem of unsatisfactory fuel consumption which is caused from the fast growth of coating. If the scale of the apparatus is enlarged, the foregoing problems of the direct drop and undesirable discharge of the raw material powder become critical. What is worse, the height of a free board of the spouted bed granulating furnace cannot be shortened. Furthermore, pressure loss becomes enlarged excessively.
A spouted bed granulating furnace has been disclosed (for example, in Japanese Utility Model Unexamined Publication No. 4-110395) in which a cone portion is formed in the lower portion, the foregoing throat portion of the spouted bed granulating furnace connected to the fluidized bed sintering furnace is formed into a porous perforated structure, opposing burners are disposed above the porous perforated structure, and a diagonal chute for supplying pre-heated raw material powder is disposed above the cone portion to face downwards.
Although the porous perforated structure of the throat portion of the spouted bed granulating furnace according to the foregoing disclosure is able to overcome the problem of the direct drop and the undesirable discharge of the raw material powder, the size of the throat cannot be enlarged satisfactorily because the local hot region must be formed in the central portion to maintain the granulating performance. What is worse, the pressure loss is increased excessively by enlarging the scale satisfactorily (a second problem).
As another conventional technology, a method of operating a granulating furnace for the purpose of controlling the granulated grain size in the spouted bed fluidized bed granulating furnace to a certain range has been disclosed, as shown in FIG. 34. According to the foregoing disclosure, a Roots blower is provided for each of a fluidized bed cooler serving as a primary cooling means and a packed bed cooler serving as a secondary cooling means and the air quantity of each of the Roots blowers is controlled so that the space velocity U0 of each of the sintering furnace and the fluidized bed cooler is made constant (see, for example, Japanese Patent Unexamined Publication No. 63-61883 and Japanese Patent Unexamined Publication No. 2-229745).
The foregoing operation method cannot control the grain size to a certain range by absorbing disturbances occurring during operation, such as, change in the components of the raw material or change in the flow of the raw material. If the grain size is decreased, the grains are agglomerated in the sintering furnace. If the grain size is enlarged, a defect takes place in fluidization. In the foregoing cases, the operation cannot be stably and continuously performed, requiring that the operation be stopped and cleaning be performed (a third problem).
Another conventional technology about a perforated distributor of a granulating furnace has been disclosed (for example, in Japanese Utility Model Unexamined Publication No. 60-10198, Japanese Patent Unexamined Publication No. 1-254242 and Japanese Patent Unexamined Publication No. 1-284509) in which nozzles having the same diameter are disposed uniformly on the overall surface of the distributor.
The raw material powder fluidized bed sintering furnace disclosed in Japanese Utility Model Unexamined Publication No. 60-10198 comprises the nozzles uniformly disposed on the overall surface of the distributor. The foregoing structure of the distributor is employed as well to form the granulating furnace so that the bed temperature of the granulating furnace is made uniform. As a result, coating can easily be generated on the wall surface on the inside layer of the granulating furnace as shown in FIGS. 35 and 36. That is, the fact that the diameter of the jet stream emitted through the outermost-nozzle is smaller than the nozzle pitch as shown in FIG. 36 causes coating as shown in the drawing. If large-diameter grains are generated in the granulating furnace, the grains cannot be discharged from the granulating furnace but they are accumulated on the distributor. As a result, fluidization encounters a defect, causing fluctuations in the operation over a period of time.
The fluidized bed reaction apparatus disclosed in Japanese Patent Unexamined Publication No. 1-254242 is different from the granulating furnace forms circulating flows of grains which move upwards in the periphery and which move downwards at the central portion by enlarging the degree of opening of the nozzles in the periphery. However, to assure granulating in the granulating furnace the periphery of the furnace should be formed into a cone structure and needs a downward flow in the moving bed. In order to maintain a certain downward movement speed, the degree of opening of the periphery nozzle must be the same or smaller than that at the central portion.
The gas distributor disclosed in Japanese Patent Unexamined Publication No. 1-284509 is enabled to make grains in the overall body of the fluidized bed form an eddy current by disposed caps respectively disposed on the nozzles and jetting out gas in one direction. Since the length of the jet stream gas is several hundred millimeters in the foregoing means, adhesion of grains to the side wall of the distributor cannot be prevented although adhesion to the top surface of the same can be prevented by the eddy current of the grains (a fourth problem).
A conventional apparatus for sintering cement clinker is known which has an arrangement made as shown in FIG. 37 such that pre-heated raw material powder of cement is, by gravitation, charged from a lowermost cyclone forming a suspension pre-heater to a position above the hopper of a jet fluidized bed granulating furnace (see, for example, Japanese Patent Unexamined Publication No. 63-60134 and Japanese Patent Unexamined Publication No. 62-225888).
In the conventional example shown in FIG. 37, charged (supplied) grains adjacent to an opening portion of the supply chute (on the upper wall surface of the cone portion) are in a full charged state and moved downwards along the wall surface of the cone portion. The charged raw materials are not dispersed but they reach the upper surface of the distributor because grains are moved. The movement speed at this time is too slow to prevent adhesion and growth of a portion of the raw material on the wall surface. Even if the supply chute from the cyclone is formed into a plurality of chutes to divide the injection, the foregoing problem cannot be overcome, and forming the coating is complicated. There has arisen another problem in that both seal air and the air curtain means from the nozzle are able to prevent back flow of grains but they cannot prevent coating because the raw material is dropped by gravitation in a state-where the raw material is not dispersed in the air (a fifth problem).
The fluidized bed furnace is, as a general rule, a container that fluidizes granular raw material by a fluid, such as a gas, which is introduced from the bottom portion thereof to cause reactions or heat exchange to take place between the raw material and the fluid. Since the raw material is brought into contact with the gas or the like over a wide surface area in the fluidized bed furnace, an excellent reaction efficiency or the like can be realized as compared with the rotary kiln. Therefore, it has been considered that the fluidized bed furnace has an advantage in reducing the space needed to install the facility, decreasing the needed fuel consumption and preventing generation of harmful exhaust gas. In order to capture granular raw material mixed with the discharge gas to again inject it into the furnace and to realize other purposes, a cyclone is usually connected to a gas discharge port of the fluidized bed furnace. At least a portion of the raw material is charged into the fluidized bed furnace through the foregoing cyclone.
However, the fluidized bed furnace receives the gas under conditions that the raw material can be fluidized, and therefore the pressure in the fluidized bed furnace is higher than that in the cyclone disposed downstream. Therefore, injection of the raw material cannot easily be performed from the cyclone to the fluidized bed furnace. If a raw material supply chute extending downwards from the cyclone is directly connected to the fluidized bed furnace, the gas is introduced (allowed to flow back) from the fluidized bed furnace into the cyclone with the raw material pushed back. What is worse, an upward blow in the cyclone makes the capture of the raw material difficult. The foregoing fact is an inevitable problem occurring due to the characteristic of the fluidized bed furnace arranged in such a manner that granules, each of which has a small size and light weight unit, are charged into the high pressure furnace as the raw material.
Accordingly, the conventional structure is arranged in such a manner that a double opening/closing damper 564 is, as shown in FIG. 38, disposed at ah intermediate position of a raw material powder supply chute 567 arranged from a cyclone 563 to a fluidized bed furnace 561. While closing at least either of two dampers 564a and 564b connected in series to prevent the back flow (the blow up) of the gas, they are opened sequentially one by one so that the raw material powder is dropped. Specifically, the upper damper 564a is opened in a state where the lower damper 564b is closed, and then the upper damper 564a is closed and the lower damper 564b is opened. As a result, the raw material is intermittently dropped into the supply chute 567 in such a manner that the capacity between the two dampers 564a and 564b is the maximum discharge quantity per cycle. Then, the raw material powder is charged into the furnace 561 by the gravitation.
The example shown in FIG. 38 shows a portion of a cement clinker manufacturing apparatus disclosed in Japanese Patent Unexamined Publication No. 62-230657. Referring to FIG. 38, reference numeral 561 represents a granulating furnace (although it is a so-called spouted bed type furnace having no perforated plate, it is included in a category of a fluidized bed furnace in a broad sense). Reference numeral 573 represents a sintering furnace (which is as well as a fluidized bed furnace), 563 and 571 represent cyclones, 572 represents a damper, and 574 and 575 represent units for downstream discharging of granules, the discharge units 574 and 575 being known hermetic discharge units (so called "L valves") that realize sealing characteristics by using the granules accumulated therein.
The double opening/closing damper 564 shown in FIG. 38 cannot completely interrupt the gas flowing back from the fluidized bed furnace 561 to the cyclone 563 by way of the chute 567. The reason for this is that a portion of the granules are caught or held in a sealing portion (a space between a valve and a seating surface with which the valve is in contact) in the damper 564 results in the sealing characteristics of the foregoing portion not always being maintained. In particular, the raw material can easily be caught in the sealing portion when the lower damper 564b is closed and the upper damper 564a is opened to accumulate the raw material therein and then the damper 564a is closed after the upper damper 564a has been filled with the raw material. If raw material is caught in the sealing portion, a gap is inevitably created adjacent to the raw material thus-caught. As a result, the gas flows backwards through the gap toward the cyclone 563. Therefore, the injection of the raw material into the fluidized bed furnace 561 usually encounters a difficulty or the raw material capturing efficiency deteriorates (a sixth problem).
Cement clinker is manufactured by a method comprising the steps of granulating raw material powder obtained by blending and grinding lime stone, quartz sand, etc. and sintering the granules and cooling the sintered granules. FIG. 32 is a view which illustrates the schematic system of a cement clinker manufacturing apparatus (partially including a new matter) of the foregoing type. Referring to FIG. 32, reference numeral 610 represents a granulating furnace, 603 represents a sintering furnace, and 604 and 605 represent cooling units (coolers) which are arranged as described later. As the granulating furnace 610 and the sintering furnace 603, fluidized bed furnaces as illustrated are widely employed in recent years. The reason for this can be described as follows: the fluidized bed furnace in general exhibits excellent reaction efficiency or the like as compared with a rotary kiln and realizes advantages in terms of the facility space reduction and the cause of prevention of harmful exhaust gas.
The raw material powder is pre-heated when it is passed through a suspension pre-heater 601, and it is charged into the granulating furnace 610 so that it is made to be grains (granulated material) each having a diameter of several millimeters while being fluidized. The raw material powder is fluidized by the hot gas and a portion of the grains present adjacent to the surface is melted in a heated state as to be allowed to adhere to one another so that the grains grow to respectively have a predetermined grain size. In this case, the sizes of the grains (that is, sizes of the granulated material) must be made to be adaptable to the specifications of the equipment and the type of the cement. If the size of the granulated material is too large, the usual air quantity (the quantity of hot air supplied from the cooling units 604 and 605) is insufficient to fluidize granulated raw material in the granulating furnace 610 and the sintering furnace 603 disposed downstream of the granulating furnace 610. As a result, combustion and/or sintering cannot be performed adequately. If the size is too small, adhesion of granules proceeds excessively in the sintering furnace 603, and therefore undesirable agglomeration takes place.
Since the grain size is varied due to various disturbances, an adequate control means must be employed. Hitherto, the control has been performed by changing the temperature of the fluidized bed 610a, the quantity of the raw material powder charged and the time in which the raw material powder (granulated material) is retained in the furnace. Although the mechanism of the granulation has not been determined yet, it has been found from experience that raising the temperature of the fluidized bed and the lengthening of the retaining time enlarge the grain size and increasing the charged raw material powder reduces the grain size.
The conventional control involving changing the temperature of the fluidized bed, the quantity of the charged raw material or the retention time in the furnace suffers from unsatisfactory response such that it takes too long a time from the moment at which the control (the input of the control) is performed to the moment at which the control is effected. Although the response time varies depending upon the type and the capacity of the granulating furnace, it takes two to four hours in a usual cement clinker sintering furnace having a diameter of 2 to 3 m. If the response is unsatisfactorily slow, the quantity of control usually cannot be made adequately. As a result, the control cannot be performed adequately and the control cannot easily be automated. Therefore, a problem arises in that needed operations become too complicated. As well as the process for manufacturing cement clinker, the foregoing problems arise commonly in a variety of cases in which raw material powder is partially melted in a fluidized bed to adhere to one another so as to be granulated so that a predetermined grain size is realized (a seventh problem).